mm, oom_reaper: do not attempt to reap a task more than twice

oom_reaper relies on the mmap_sem for read to do its job.  Many places
which might block readers have been converted to use down_write_killable
and that has reduced chances of the contention a lot.  Some paths where
the mmap_sem is held for write can take other locks and they might
either be not prepared to fail due to fatal signal pending or too
impractical to be changed.

This patch introduces MMF_OOM_NOT_REAPABLE flag which gets set after the
first attempt to reap a task's mm fails.  If the flag is present after
the failure then we set MMF_OOM_REAPED to hide this mm from the oom
killer completely so it can go and chose another victim.

As a result a risk of OOM deadlock when the oom victim would be blocked
indefinetly and so the oom killer cannot make any progress should be
mitigated considerably while we still try really hard to perform all
reclaim attempts and stay predictable in the behavior.

Link: http://lkml.kernel.org/r/1466426628-15074-10-git-send-email-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 36d5dd88d990..bfddc93ccd34 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -556,8 +556,27 @@ static void oom_reap_task(struct task_struct *tsk)
 		schedule_timeout_idle(HZ/10);
 
 	if (attempts > MAX_OOM_REAP_RETRIES) {
+		struct task_struct *p;
+
 		pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
 				task_pid_nr(tsk), tsk->comm);
+
+		/*
+		 * If we've already tried to reap this task in the past and
+		 * failed it probably doesn't make much sense to try yet again
+		 * so hide the mm from the oom killer so that it can move on
+		 * to another task with a different mm struct.
+		 */
+		p = find_lock_task_mm(tsk);
+		if (p) {
+			if (test_and_set_bit(MMF_OOM_NOT_REAPABLE, &p->mm->flags)) {
+				pr_info("oom_reaper: giving up pid:%d (%s)\n",
+						task_pid_nr(tsk), tsk->comm);
+				set_bit(MMF_OOM_REAPED, &p->mm->flags);
+			}
+			task_unlock(p);
+		}
+
 		debug_show_all_locks();
 	}